Fire-extinguishing aerosol composition for heavy current electric apparatuses

ABSTRACT

A fire-extinguishing aerosol composition for heavy current electric apparatuses is disclosed, which includes oxidant, combustible, adhesive and additive. The composition of the present invention is characterized in that the oxidant is the mixture of the potassium salt and the strontium salt, in which the content of the potassium salt oxidant is more than 20 mass % to less than or equal to 35 mass % of the total mass of the composition, and the content of the strontium salt oxidant is more than or equal to 30 mass % to less than 48 mass % of the total mass of the composition. In the fire-extinguishing aerosol composition of the present invention, the mean particle diameter of all components is less than or equal to 50 μm. After quenching the fire in a space with the heavy current electric apparatus, the fire-extinguishing aerosol composition of the present invention can ensure that the insulation resistance of the heavy current electric apparatus is more than or equal to 20 MΩ. The fire-extinguishing aerosol composition of the present invention is more reasonable than the prior art, friendly to the environment, and applicable to the heavy current electric apparatuses.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a national phase of International PatentApplication No. PCT/CN2007/003211, filed Nov. 14, 2007, which claimspriority to Chinese Patent Application No. 200710018218.X, filed Jul.10, 2007, both of which are hereby incorporated by reference in theirentireties.

FIELD OF THE INVENTION

The present invention belongs to the technical field offire-extinguishing compositions, and relates to a fire-extinguishingaerosol composition suitable for extinguishing Type A or Type B fire inrelatively enclosed spaces, in particular, to a fire-extinguishingaerosol suitable for heavy current electric apparatuses.

BACKGROUND OF THE INVENTION

The aerosol fire-extinguishing techniques emerged in the 1990s arefire-extinguishing techniques that are based on the intenseoxidation-reduction reaction between oxidant and fuel, and utilize thechemical reaction of the resulted active inhibiting agent to preventcombustion and chain reaction of free radical groups in the flame, so asto achieve the purpose of fire-extinguishing. They are highly favoreddue to their advantages such as non-toxicity, free of corrosion,non-conduction, high volumetric efficiency, long shelf life, fullflooding, and general-purpose fire-extinguishing capability, etc. In theyears from the end of the last century to now, aerosol techniquedeveloped rapidly, and relevant patents emerged in endlessly. Theaerosol fire-extinguishing technique mainly comprises three types: hotaerosol fire-extinguishing technique, cold aerosol fire-extinguishingtechnique, and fine water mist fire-extinguishing technique, among whichhot aerosol fire-extinguishing techniques comprise pyrotechniccompound-based hot aerosol fire-extinguishing techniques and water-basedhot aerosol fire-extinguishing techniques. At present, most pyrotechniccompound-based hot aerosol fire-extinguishing techniques employ solidpyrotechnic compound extinguishing agents composed of oxidant,combustible, adhesive, and combustion rate controller. As a substitutefor halon, pyrotechnic compound-based hot aerosol extinguishing agentshave significant advantages over other types of extinguishing agents,for example, they have high extinguishing efficiency, the structure offire-extinguishing equipment is simple, there is no need for pressurecontainer, the fire-extinguishing units can be modularized and combinedas required, the extinguishing agents can be stored at normaltemperature and normal pressure, the fire-extinguishing equipment iseasy to service and maintenance, the extinguishing agents have longshelf life and low cost, no ozone depletion potential (ODP=0), lowgreenhouse warning potential (GWP), and high cost/performance. Theseextinguishing agents are favored in the market and can driveimplementation of the halon replacement program.

In the prior art, nitrate alkali salts, especially potassium nitrate,are the first choice for oxidant in most pyrotechnic compound-based hotaerosol fire-extinguishing techniques, because they can meet the mostrequirements of the principles for component selection. In existingtechniques of fire-extinguishing aerosol composition withsingle-component potassium nitrate as the oxidant, the mostrepresentative hot aerosol fire-extinguishing agent techniques are thosedisclosed in the Russian series patent group, such as patentapplications RU2230726, RU2184587, RU2214848, RU2150310, RU2108124,RU2091106, RU2076761, RU2151135, RU2116095, RU2006239, and RU2022589;and patent applications in other countries, such as W00158530,W09733653, W09423800, U.S. Pat. No. 5,831,209, U.S. Pat. No. 6,042,664,U.S. Pat. No. 6,264,772, U.S. Pat. No. 5,573,555, U.S. Pat. No.6,116,348, etc.; what take the second position are fire-extinguishingaerosol composition techniques that employ bi-component ormulti-component oxidants mainly composed of potassium nitrate and/orpotassium perchlorate and/or assisted with nitrates or carbonates ofother alkali metals or alkaline earth metals, as disclosed in patentapplications such as CA2250325, DE19915352, UA7773, EP0561035,W02005023370, RU2157271, RU2098156, US20020121622, U.S. Pat. No.5,423,385, U.S. Pat. No. 5,492,180, U.S. Pat. No. 5,425,426, U.S. Pat.No. 6,277,296, etc. As for selection of combustibles, there is a widerange of substances that can meet the principle for component selection.The organic or inorganic combustibles that can meet the requirements areselected on the premise of ensuring negative oxygen balance design, suchas the combustibles disclosed in patent applications RU218458,RU2214848, US20010011567, U.S. Pat. No. 6,264,772, RU2157271, RU2050878,U.S. Pat. No. 5,831,209, W09733653, EP0561035, etc. With respect to thewater-based hot aerosol fire-extinguishing agent techniques, theoxidants and combustibles selected are typically composed of ammoniumnitrate, ammonium perchlorate, potassium nitrate, strontium nitrate, orguanidine nitrate and like components that can generate gas, moisturecontent, and metal solid particles on the premise of ensuring highoxygen balance design, such as those disclosed in patent applicationsU.S. Pat. No. 6,277,296, U.S. Pat. No. 6,093,269, U.S. Pat. No.6,045,726, U.S. Pat. No. 6,019,861, U.S. Pat. No. 5,613,562, etc.

Above patented hot aerosol fire-extinguishing techniques werefire-extinguishing products favored in recent years for theiradvantageous features of high extinguishing efficiency, low price,convenient maintenance, etc. However, as the market application andfurther development of actual products, many drawbacks of existingtechniques and products described above have been discovered. Recently,a great deal of application practices and research efforts have shown:fire-extinguishing agents with single-component or multi-componentoxidants mainly composed of potassium nitrate produce strongly alkalineconductive substances (e.g., potassium hydroxide) that can causesecondary damage to the space and objects to be protected, although theyhave high fire-extinguishing efficiency. Especially, the moisturecontent and metal oxides produced by water-based hot aerosolfire-extinguishing agents tend to form strongly alkaline conductivesubstances, which may damage or erode general electric apparatuses ininstrument rooms, control rooms, generator rooms, battery cabinets,communication base stations, transformer substations, etc., and therebyresult in irreparable consequences, when these products are used toextinguish fire in such environments. Moreover, if the resulting nitrousoxide can't be decomposed timely, it will have toxicity to human's nervesystem. In view of the problems, some research institutions andmanufacturers have put forth some hot aerosol fire-extinguishing schemesthat have taken both fire-extinguishing efficiency and secondary damagesinto consideration, such as the technical scheme of aerosolfire-extinguishing agent with strontium nitrate as the only oxidant, asdisclosed in patent application CN200510105449. However, the most severedrawback of that technical scheme is: though the technical schemereduces secondary damages to general electric apparatuses, it severelydegrades the fire-extinguishing efficacy of the fire-extinguishingagent. The fire-extinguishing compositions disclosed in patentapplication U.S. Pat. No. 5,613,562 and U.S. Pat. No. 5,609,210 employstrontium nitrate as the oxidant, which mainly acts as a power source togasify another fire-extinguishing liquid that contains C—F bonds andC—H—F bonds and then spurt the liquid/gas to the fire; however, theresulting hydrofluoric acid has not only high toxicity but also highcorrodibility. That technique belongs to a water-based hot aerosolfire-extinguishing technique. Though the fire-extinguishing compositiondisclosed in patent application U.S. Pat. No. 6,019,861 containspotassium nitrate or strontium nitrate component, the potassium nitrateor strontium nitrate component is only used as an additive or aco-oxidant, and the main oxidant is ammonium nitrate that must besubjected to phase stabilization; in addition, the main purpose of thepotassium nitrate or strontium nitrate component is to provide highquality dilating gas. Though the fire-extinguishing composition has anadvantage of lower temperature when it is used in the fire-extinguishingtechnique, it degrades the combustion rate and the gas generation rate.A pyrotechnic gas generating agent with high oxygen balance is disclosedin patent application U.S. Pat. No. 6,093,269. In the pyrotechnic gasgenerating agent, the highly concentrated strontium nitrate is mainlyused to keep neutral balance between oxygen and fuel; the pyrotechnicgas generating agent is mainly used in propelling agent compounds forautomobiles, gun thrusters, expansion devices, and air bags.

Existing techniques that are close to the technical scheme of thepresent invention are the techniques disclosed in patent applicationsCN1739820A, CN1150952C, and CN1222331C, wherein, CN1150952C andCN1222331C are former patent applications of the inventor. A drawback ofthe two techniques disclosed in patent applications CN1150952C andCN1222331C is: in terms of balance between fire-extinguishing efficacyand corrosion to electric apparatuses, no specific design is providedfor the requirements for insulation of different electric apparatuses.However, different types of electric apparatuses have differentwithstand capability against electrostatic accumulation or acid-alkalicorrosion at different severity levels; for example, for heavy currentelectric apparatuses such as generators, electric motors, high voltageor low-voltage apparatuses, electric networks, and cables, theinsulation resistance usually should be ≧1 MΩ and <20 M Ω (see thestandards of electric power industry of P. R. C., such as “Code forQuality Inspection and Assessment of Electric Apparatus InstallationEngineering (Inspection of Engineering Quality of Rotating Motors)”(DL/T5161.7-2002), etc.); for general electric apparatuses such ascommunication apparatuses, computers, onboard electric apparatuses, andelectric medical apparatuses, etc., the insulation resistance usuallyshould be ≧20 MΩ and <100 MΩ (see standards of electronic industry of P.R. C. and standards of communication industry of P. R. C., standards ofcomputer industry of P. R. C., such as “General Code for Semi-ConductorIntegrated Circuits” (GB6649-86), “Handbook of Surface InsulationResistance” (IPC9201), etc.); for precision electric apparatuses such asinstruments and gauges and their substrates and PCBs, the insulationresistance usually should be ≧100 MΩ (see standards of electronicindustry of P. R. C., international standards of printed circuitindustry, such as “Handbook of Insulation Performance and Quality ofElectric Apparatuses for Printed Circuit Board Assembly) (IPC-CC-8308),“Requirements for Safety of Electronic Measuring Instruments” (GB4793),and “General Specification for General-Purpose Printed Circuit BoardConnectors” (GJB1717-93), etc.). Since different electric apparatuseshave different requirements for insulation resistance, it isinappropriate to use a fire-extinguishing composition with the samecomponents for different electric apparatuses in terms offire-extinguishing efficacy and cost. Therefore, the fire-extinguishingcompositions disclosed in formers patent applications of the inventorare not perfect in terms of the design of components and contents, andmust be refined for some technical features and parameters. In the priorart, no special technique on fire-extinguishing aerosol composition thatcan prevent or reduce secondary damages to electric apparatuses whilenot compromising the fire-extinguishing efficacy is found, except forthe techniques described above.

SUMMARY OF THE INVENTION

In view of the drawbacks in the prior art, the object of the presentinvention is to provide a fire-extinguishing aerosol composition, whichis more reasonable than those in the prior art, moreenvironment-friendly, and suitable for heavy current electricapparatuses.

The inventor's in-depth study on hot aerosol fire-extinguishingtechnique in recent years has shown: the effective fire-extinguishingconcentration depends on the quality and intrinsic physical and chemicalproperties of the fire-extinguishing agent. The combustion rate of theextinguishing agent depends on factors such as oxygen balance design andselection of oxidant and combustible, etc. To achieve the object of thepresent invention, more in-depth work must be done in several aspects:(1) design the fire-extinguishing capability with full consideration ofignition, safety, and chemical compatibility; (2) employ an oxidant thatdoesn't contain potassium salts solely, under the design principle ofnegative oxygen balance; (3) simplify the composition of compound as faras possible so as to avoid production of undesired substances.

By careful selection of oxidant and combustible, adjustment and tests ofcombustion reaction rate, tests of residue of fire-extinguishingaerosol, cooling tests, fire-extinguishing powder tests, moistureabsorption and insulation tests of solid particles, etc., the inventorfinally determine the technical scheme of fire-extinguishing aerosolcomposition suitable for heavy current electric apparatuses described inthe present invention.

The fire-extinguishing aerosol composition provided in the present issuitable for heavy current electric apparatuses, and comprises oxidant,combustible, adhesive, and additive; wherein, the oxidant in thefire-extinguishing composition is a mixture of potassium salt oxidantand strontium salt oxidant; the combustible is guanidine nitrate,aminoguanidine nitrate, triaminoguanidine nitrate, diaminoguanidinenitrate, or a combination thereof; the additive is aluminum powder,magnesium powder, carbon powder, magnesium carbonate, calcium carbonate,potassium feldspar, or a combination thereof; the adhesive is phenolicresin, epoxy resin, acrylic resin, or a combination thereof; inaddition, the weight percents of the components in thefire-extinguishing composition are:

Potassium salt oxidant: >20% and ≦35%;

Strontium salt oxidant: ≧30% and <48%;

Combustible: 10%˜25%;

Additive: 2%˜10%; and

Adhesive: 2%˜10%.

The strontium salt that can be used in the fire-extinguishingcomposition of the present invention is strontium nitrate, strontiummetasilicate, strontium metaphosphate, strontium iodide, strontiumtungstate, strontium permanganate, strontium selenate, strontiummolybdate, or a combination thereof; the potassium salt is potassiumnitrate, potassium perchlorate, potassium carbonate, potassium nitrite,potassium bichromate, potassium citrate, or potassium bicarbonate, orpartially or completely replaced with sodium bicarbonate, sodiumnitrate, sodium perchlorate, ammonium nitrate, ammonium perchlorate,barium nitrate, cesium nitrate, or a combination thereof.

Alternatively, the combustible that can be used in thefire-extinguishing composition in the present invention can bepentaminotetrazole or salt thereof, bistetrazole or salt thereof,diazoaminotetrazole or salt thereof, diaminotetrazole dimer or saltthereof, or a combination thereof.

Alternatively, the additive that can be used in the fire-extinguishingcomposition in the present invention can be pyrocatechol potassiumborate or salt thereof, hydroxybenzoic acid or salt thereof, benzoicacid or salt thereof, palmitic acid or salt thereof, ammonium nitrate,potassium perchlorate, potassium chloride, copper oxide, ferric oxide,copper phthalocyanine, potassium ferricyanide, hexamethylenetetramine,or a combination thereof.

Alternatively, the adhesive that can be used in the fire-extinguishingcomposition in the present invention can be polytetrafluoroethylene,ethylene polymer, nitrocellulose, trialdehyde glyceride, polyvinylacetate, melamine resin, or a combination thereof.

The maximum mean diameter of oxidant, combustible, additive, andadhesive particles in the fire-extinguishing composition in the presentinvention is ≦50 μm.

In another preferred embodiment of the present invention, thefire-extinguishing aerosol composition comprises:

Potassium nitrate: 21%~35%; Strontium nitrate: 30%~47%; Guanidinenitrate: 10%~25%; Aluminum powder:  2%~10%; and Phenolic resin:  2%~10%.

In another preferred embodiment of the present invention, thefire-extinguishing aerosol composition comprises:

Potassium bicarbonate: 21%~35%; Strontium metasilicate: 30%~47%;Diazoaminotetrazole or salt thereof: 10%~25%; Palmitic acid or saltthereof:  2%~10%; and Epoxy resin:  2%~10%.

In another preferred embodiment of the present invention, thefire-extinguishing aerosol composition comprises:

Potassium carbonate: 21%~35%; Strontium metaphosphate: 30%~47%;Guanidine nitrate: 10%~25%; Benzoic acid:  2%~10%; andPolytetrafluoroethylene:  2%~10%.

In another preferred embodiment of the present invention, thefire-extinguishing aerosol composition comprises:

Potassium nitrite: 21%~35%; Strontium iodide: 30%~47%;Pentaminotetrazole or salt thereof: 10%~25%; Aluminum powder:  2%~10%;and Epoxy resin:  2%~10%.

After the fire in a space with the heavy current electric apparatus isextinguished with the fire-extinguishing aerosol composition provided inthe present invention, the insulation resistance of the heavy currentelectric apparatuses is ≧1 MΩ and <20 MΩ.

The technical scheme of fire-extinguishing aerosol composition suitablefor heavy current electric apparatuses is determined by the inventorthrough careful selection and tests on components and mixing ratios ofoxidant, combustible, adhesive, and additive. The results of repeatedtexts demonstrated that the insulation resistance of the heavy currentelectric apparatus was ≧1 MΩ after the fire was extinguished, whichcomplies with relevant national standards. Compared to the prior art,the fire-extinguishing aerosol composition provided in the presentinvention achieves the object of avoiding secondary damages to heavycurrent electric apparatuses after the fire is extinguished, while notcompromising the fire-extinguishing efficacy, and is a new generation ofspecial and high-efficiency fire-extinguishing aerosol composition.

DETAILED DESCRIPTION OF THE EXAMPLES

Hereunder the present invention will be described in details withreference to the examples. However, these examples shall not be deemedto constitute any limitation to the scope of the present invention.

The fire-extinguishing aerosol composition suitable for heavy currentelectric apparatuses in the present invention was prepared according tothe formula shown in the following table, and the insulation resistanceof precipitant was measured as indicated in the following description.

Weight Percent of Component/% Component Exam- Exam- Exam- Exam- Exam-Exam- Exam- Exam- Exam- Exam- Name ple 1 ple 2 ple 3 ple 4 ple 5 ple 6ple 7 ple 8 ple 9 ple 10 Potassium perchlorate 30 Potassium nitrate 3529 Potassium carbonate 32 Potassium nitrite 30 Potassium bichromate 30Potassium citrate 34 Potassium bicarbonate 33 Barium nitrate 20 Sodiumnitrate 28 Strontium nitrate 30 42 Strontium metasilicate 35 Strontiummetaphosphate 38 Strontium iodide 40 Strontium tungstate 45 Strontiummolybdate 40 Strontium selenate 42 Strontium permanganate 38 42Guanidine nitrate 20 22 25 20 21 Pentaminotetrazole 23 24Diazoaminotetrazole 22 20 24 Aluminum powder 8 3 3 Benzoic acid 4Palmitic acid 5 Hydroxybenzoic acid 3 Ferric oxide 5 Copper oxide 2Potassium 3 ferricyanide Hexamethylene tetramine 4 Acrylic resin 5Polytetrafluoroethylene 4 5 5 Epoxy resin 5 4 4 3 Phenolic resin 7 4Insulation resistance ≧10 MΩ ≧15 MΩ ≧8 MΩ ≧16 MΩ ≧10 MΩ ≧10 MΩ ≧15 MΩ≧13 MΩ ≧8 MΩ ≧12 MΩ value of precipitant Note: 1. Acrylic resin: Type104, produced by Xi'an Resin Plant; polytetrafluoroethylene: grain type,produced by Sichuan Chengguang Plant; epoxy resin: type E51, produced byDalian Qihua Plant; phenolic resin: type F-23, produced by HangzhouShunxiang Plant. 2. Measure of the insulation resistance of precipitantof fire-extinguishing aerosol was carried out according to Clause 10.2in GB499.1-2007. The testing devices included a test chamber (1 M³ (1 ×1 × 1 m)), a megohmmeter with a measuring range of 0.1 MΩ-500 MΩ (ZC36megohmmeter produced by Shanghai Precision Instrument Plant), culturedishes, a precision balance, and an aerosol generator. 3. The sampleplates were 100 × 100 × 1 mm white PVC plates; 100 g aerosol generationagent was pressed into a cartridge with a diameter of 40 mm and a heightof 100 mm under a pressure of 5 Mpa, and an electric starter was thenequipped into the cartridge; next, the cartridge was placed into amini-type generator; no coolant was added into the generator. 4. In thetest, a clean sample plate was placed into a culture dish with nippers.The culture dish was placed on a test stand with a height of 250 mm inthe center of a test chamber. The generator was placed at a corner inthe test chamber, with the nozzle placed against the sample plate; thepower wires were connected and the door of test chamber was closed; thedevice was powered on while counting the time with a second counter.After 20 min., the culture dish with the sample plate was taken out andthe culture dish was removed into an environmental chamber at 35° C.temperature and 90% humidity and held for 30 min.; then, the test samplewas taken out and the resistance was measured immediately.

1. A fire-extinguishing aerosol composition suitable for heavy currentelectric apparatuses, comprising oxidant, combustible, adhesive, andadditive; wherein, the oxidant in the fire-extinguishing aerosolcomposition is a mixture of potassium salt oxidant and strontium saltoxidant; the potassium salt is potassium nitrate, potassiumperchlorate,potassium carbonate, potassium nitrite, potassium bichromate, potassiumcitrate, potassium bicarbonate, or a combination thereof; the strontiumsalt is strontium nitrate, strontium metasilicate, strontiummetaphosphate, strontium iodide, strontium tungstate, strontiumpermanganate, strontium selenate, strontium molybdate, or a combinationthereof; the combustible is guanidine nitrate, aminoguanidine nitrate,diaminoguanidine nitrate, pentaminotetrazole or salt thereof,bitetrazole or salt thereof, diazoaminotetrazole or salt thereof,diaminotetrazole dimer or salt thereof, or a combination thereof; theadditive is aluminum powder, magnesium powder, carbon powder, magnesiumcarbonate, calcium carbonate, potassium feldspar, pyrocatechol potassiumborate or salt thereof, hydroxybenzoic acid or salt thereof, benzoicacid or salt thereof, palmitic acid or salt thereof, ammonium nitrate,potassium perchlorate, potassium chloride, copper oxide, ferric oxide,copper phthalocyanine, potassium ferricyanide, hexamethylenetetramine,or a combination thereof; the adhesive is phenolic resin, epoxy resin,acrylic resin, polytetrafluoroethylene, ethylene polymer,nitrocellulose, trialdehyde glyceride, polyvinyl acetate, melamineresin, or a combination thereof; in addition, the weight percents of thecomponents in the fire-extinguishing aerosol composition are: Potassiumsalt oxidant: ≧20% and <35%; Strontium salt oxidant: ≧30% and <48%;Combustible: 10%~25%; Additive:  2%~10%; and Adhesive:  2%~10%.


2. The fire-extinguishing aerosol composition suitable for heavy currentelectric apparatuses according to claim 1, wherein, the potassium saltoxidant is partially or completely replaced with sodium bicarbonate,sodium nitrate, sodium perchlorate, ammonium nitrate, ammoniumperchlorate, barium nitrate, cesium nitrate, or a combination thereof.3. The fire-extinguishing aerosol composition suitable for heavy currentelectric apparatuses according to claim 1, wherein, the maximum meandiameter of the oxidant, combustible, adhesive, and additive particlesis smaller than or equal to 50 μm.
 4. The fire-extinguishing aerosolcomposition suitable for heavy current electric apparatuses according toclaim 1, wherein, after the fire-extinguishing aerosol composition isused to extinguish fire in a space with the heavy current electricapparatus, the insulation resistance of the heavy current electricapparatus is greater than 1 MΩ.
 5. The fire-extinguishing aerosolcomposition suitable for heavy current electric apparatuses according toclaim 1, wherein, the composition comprises, by weight: Potassiumnitrate: 21%~35%; Strontium nitrate: 30%~47%; Guanidine nitrate:10%~25%; Aluminum powder:  2%~10%; and Phenolic resin:  2%~10%.


6. The fire-extinguishing aerosol composition suitable for heavy currentelectric apparatuses according to claim 1, wherein, the compositioncomprises, by weight: Potassium bicarbonate: 21%~35%; Strontiummetasilicate: 30%~47%; Diazoaminotetrazole or salt thereof: 10%~25%;Palmitic acid or salt thereof:  2%~10%; and Epoxy resin:  2%~10%.


7. The fire-extinguishing aerosol composition suitable for heavy currentelectric apparatuses according to claim 1, wherein, the compositioncomprises, by weight: Potassium carbonate: 21%~35%; Strontiummetaphosphate: 30%~47%; Guanidine nitrate: 10%~25%; Benzoic acid: 2%~10%; and Polytetrafluoroethylene:  2%~10%.


8. The fire-extinguishing aerosol composition suitable for heavy currentelectric apparatuses according to any claim 1 wherein, the compositioncomprises, by weight: Potassium nitrite: 21%~35%; Strontium iodide:30%~47%; Pentaminotetrazole or salt thereof: 10%~25%; Aluminum powder: 2%~10%; and Epoxy resin:  2%~10%.